/****************************************************************************
 *
 * Copyright 2018 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/****************************************************************************
 * arch/arm/src/stm32/stm32_rng.c
 *
 *   Copyright (C) 2012 Max Holtzberg. All rights reserved.
 *   Author: Max Holtzberg <mh@uvc.de>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <stdint.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <debug.h>
#include <errno.h>

#include <tinyara/irq.h>
#include <tinyara/arch.h>

#include "up_arch.h"
#include "chip/stm32_rng.h"
#include "up_internal.h"

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

static int stm32_rnginitialize(void);
static int stm32_interrupt(int irq, void *context);
static void stm32_enable(void);
static void stm32_disable(void);
static ssize_t stm32_read(struct file *filep, char *buffer, size_t);

/****************************************************************************
 * Private Types
 ****************************************************************************/

struct rng_dev_s {
	sem_t rd_devsem;			/* Threads can only exclusively access the RNG */
	sem_t rd_readsem;			/* To block until the buffer is filled  */
	char *rd_buf;
	size_t rd_buflen;
	uint32_t rd_lastval;
	bool rd_first;
};

/****************************************************************************
 * Private Data
 ****************************************************************************/

static struct rng_dev_s g_rngdev;

static const struct file_operations g_rngops = {
	0,							/* open */
	0,							/* close */
	stm32_read,					/* read */
	0,							/* write */
	0,							/* seek */
	0							/* ioctl */
#ifndef CONFIG_DISABLE_POLL
	, 0						/* poll */
#endif
};

/****************************************************************************
 * Private functions
 ****************************************************************************/

static int stm32_rnginitialize()
{
	uint32_t regval;

	vdbg("Initializing RNG\n");

	memset(&g_rngdev, 0, sizeof(struct rng_dev_s));

	sem_init(&g_rngdev.rd_devsem, 0, 1);

	if (irq_attach(STM32_IRQ_RNG, stm32_interrupt, NULL)) {
		/* We could not attach the ISR to the interrupt */

		vdbg("Could not attach IRQ.\n");

		return -EAGAIN;
	}

	/* Enable interrupts */

	regval = getreg32(STM32_RNG_CR);
	regval |= RNG_CR_IE;
	putreg32(regval, STM32_RNG_CR);

	up_enable_irq(STM32_IRQ_RNG);

	return OK;
}

static void stm32_enable()
{
	uint32_t regval;

	g_rngdev.rd_first = true;

	regval = getreg32(STM32_RNG_CR);
	regval |= RNG_CR_RNGEN;
	putreg32(regval, STM32_RNG_CR);
}

static void stm32_disable()
{
	uint32_t regval;
	regval = getreg32(STM32_RNG_CR);
	regval &= ~RNG_CR_RNGEN;
	putreg32(regval, STM32_RNG_CR);
}

static int stm32_interrupt(int irq, void *context)
{
	uint32_t rngsr;
	uint32_t data;

	rngsr = getreg32(STM32_RNG_SR);

	if ((rngsr & (RNG_SR_SEIS | RNG_SR_CEIS))	/* Check for error bits */
		|| !(rngsr & RNG_SR_DRDY)) {	/* Data ready must be set */
		/* This random value is not valid, we will try again. */

		return OK;
	}

	data = getreg32(STM32_RNG_DR);

	/* As required by the FIPS PUB (Federal Information Processing Standard
	 * Publication) 140-2, the first random number generated after setting the
	 * RNGEN bit should not be used, but saved for comparison with the next
	 * generated random number. Each subsequent generated random number has to be
	 * compared with the previously generated number. The test fails if any two
	 * compared numbers are equal (continuous random number generator test).
	 */

	if (g_rngdev.rd_first) {
		g_rngdev.rd_first = false;
		g_rngdev.rd_lastval = data;
		return OK;
	}

	if (g_rngdev.rd_lastval == data) {
		/* Two subsequent same numbers, we will try again. */

		return OK;
	}

	/* If we get here, the random number is valid. */

	g_rngdev.rd_lastval = data;

	if (g_rngdev.rd_buflen >= 4) {
		g_rngdev.rd_buflen -= 4;
		*(uint32_t *)&g_rngdev.rd_buf[g_rngdev.rd_buflen] = data;
	} else {
		while (g_rngdev.rd_buflen > 0) {
			g_rngdev.rd_buf[--g_rngdev.rd_buflen] = (char)data;
			data >>= 8;
		}
	}

	if (g_rngdev.rd_buflen == 0) {
		/* Buffer filled, stop further interrupts. */

		stm32_disable();
		sem_post(&g_rngdev.rd_readsem);
	}

	return OK;
}

/****************************************************************************
 * Name: stm32_read
 ****************************************************************************/

static ssize_t stm32_read(struct file *filep, char *buffer, size_t buflen)
{
	if (sem_wait(&g_rngdev.rd_devsem) != OK) {
		return -errno;
	} else {
		/* We've got the semaphore. */

		/* Initialize semaphore with 0 for blocking until the buffer is filled from
		 * interrupts.
		 */

		sem_init(&g_rngdev.rd_readsem, 0, 1);

		g_rngdev.rd_buflen = buflen;
		g_rngdev.rd_buf = buffer;

		/* Enable RNG with interrupts */

		stm32_enable();

		/* Wait until the buffer is filled */

		sem_wait(&g_rngdev.rd_readsem);

		/* Free RNG for next use */

		sem_post(&g_rngdev.rd_devsem);

		return buflen;
	}
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

void up_rnginitialize()
{
	stm32_rnginitialize();
	register_driver("/dev/random", &g_rngops, 0444, NULL);
}
